You not only can, but you must.
If you don't, you will drown. Find outlets for your stress. Make sure you take care of yourself. It honestly doesn't require 12-14 hour days. If you're effective with your time, you could easily get by with 4-5 hours a day in addition to your two classes and still do a ton of work (I'm talking about what's required and then a lot extra). And you only need to work one day over the weekend, max.
I cannot agree more with this post. I think there is a point where you are doing more harm than good by killing yourself studying. If you are an exercise person, make time to exercise every day. It will help clear your mind. Be efficient with your study time, and with your play time. Don't mix the two.
Of course this varies based on the person. I'm not a big studier until about 3 weeks or so before the exam. I keep my head above water, and don't fall behind, but I don't think I really step it up until a few weeks before. I know if I do that, I will peak right around exam time. It might take a semester to dial this in (which sucks, I know) but once you find your sweet spot, stick with it. Don't kill yourself.